Diesel emissions are an environmental concern that has limited application of diesel engines despite the fuel efficiency offered by these engines. To reduce harmful emissions, technologies that treat the exhaust gas downstream of the engine have been developed including selective catalytic reduction systems that inject a small quantity of diesel exhaust fluid (DEF) into the exhaust upstream of a catalyst where is vaporizes and decomposes to form ammonia and carbon dioxide. The ammonia (NH3) converts nitrogen oxides (NOx) within the exhaust gas to harmless nitrogen (N2) and water (H2O). It has been estimated that DEF consumption is approximately 2% of fuel consumption within a typical diesel engine. Consequently, significant amounts of DEF must be stored in a tank or reservoir within a vehicle for dosing in the exhaust system. One DEF that has gained wide acceptance through regulation is an Aqueous Urea Solution on (AUS).
Aqueous Urea Solutions are effective in reducing nitrogen oxides (NOx) contained in the exhaust gas of an engine. One drawback, however, is the freezing temperature for Aqueous Urea Solution is about −11° C. (12° F.) placing it within the ambient temperature range of colder regions. To avoid freezing of the solution, it is known to use an electric resistance heater or heat exchanger using engine coolant to warm or thaw the Aqueous Urea Solution. The present invention improves upon these techniques.